The present invention generally relates to a pulse arc welding machine which is adapted to feed at a constant speed a welding wire as a waste electrode to turn the molten lump of the wire tip end into a spray state by a pulse current so as to effect an welding operation.
In a pulse arc welding machine which effects the constant-current control of both the conventional pulse peak current portion and base current portion, a rising grade of the pulse current from the base current portion to the pulse peak current portion and a lowering grade of the pulse current from the pulse peak current portion to the base current portion are determined by the transient characteristics of the reactor connected with the main circuit of the welding with the welding output controlling element being made full conductive or full non-conductive. In the conventional method, it is difficult to easily control the value of the reactor minutely. Under the existing circumstances, an intermediate terminal is provided on the reactor so as to cope with the problem on the spot through the manual switching operation of it especially when a problem exists with the rising, lowering grades of the same pulse current in the value of the same reactor with respect to the combination of the material quality of the welding wire, the wire diameter, the wire feeding speed.
The rising grade, the lowering grade of the pulse current apply influences upon the bead outer appearance, the gas shielding property and the welding function in accordance with the material quality of the welding wire, the wire diameter, the wire feeding speed.
The mild steel wire in the shield gas of, for example, argon+CO2 whose globules are hard to spray requires the pulse current which is larger in the grade. When the grade is small, the spraying operation is not smoothly promoted. In the wire of pure aluminum or the like which is extremely easy to spray, the bead outer appearance becomes worse, the gas shielding property is also damaged when the pulse current of the excessive grade is given, so that black oxide is likely to be separated on the bead surfaces. In the region where the average value of the welding current is a spray critical current or lower, the spraying operation has to be promoted with the pulse current larger in the grade. In the region where the average value of the welding current is a spray critical current or more, the spraying operation is easily effected, with a result that the rising, lowering grades of the excessive pulse current damage the bead outer appearances.